From 8bd46de2a681f7bfbd93778b952b06f270feab94 Mon Sep 17 00:00:00 2001
From: EvanTheProgrammer <86786575+EvanTheProgrammer@users.noreply.github.com>
Date: Thu, 16 Nov 2023 15:05:32 -0500
Subject: [PATCH] Add an example for a basic pong game with mode 3 graphics and
 drawing on vblank. (#189)

* Create mode3_pong_example_game.rs

* Update mode3_pong_example_game.rs

* Update mode3_pong_example_game.rs
---
 examples/mode3_pong_example_game.rs | 159 ++++++++++++++++++++++++++++
 1 file changed, 159 insertions(+)
 create mode 100644 examples/mode3_pong_example_game.rs

diff --git a/examples/mode3_pong_example_game.rs b/examples/mode3_pong_example_game.rs
new file mode 100644
index 00000000..67ec9cb2
--- /dev/null
+++ b/examples/mode3_pong_example_game.rs
@@ -0,0 +1,159 @@
+/* 
+* Made by Evan Goemer
+* Discord: @evangoemer
+*/
+
+#![no_std]
+#![no_main]
+
+use gba::{prelude::*, mem_fns::__aeabi_memset};
+
+const SCREEN_WIDTH: u16 = 240;
+const SCREEN_HEIGHT: u16 = 160;
+
+const PADDLE_WIDTH: u16 = 4;
+const PADDLE_HEIGHT: u16 = 20;
+const BALL_SIZE: u16 = 2;
+
+struct Paddle {
+    x: u16,
+    y: u16,
+}
+
+struct Ball {
+    x: u16,
+    y: u16,
+    dx: i16,
+    dy: i16,
+}
+
+impl Paddle {
+    fn new(x: u16, y: u16) -> Self {
+        Self {
+            x,
+            y,
+        }
+    }
+
+    fn update(&mut self) {
+        let keys = KEYINPUT.read();
+        if keys.up() && self.y > 1 {
+            self.y -= 1;
+        }
+
+        if keys.down() && self.y + PADDLE_HEIGHT + 1 < SCREEN_HEIGHT {
+            self.y += 1;
+        }
+    }
+}
+
+impl Ball {
+    fn new(x: u16, y: u16) -> Self {
+        Self { x, y, dx: 1, dy: 1 }
+    }
+
+    fn update(&mut self, paddle1: &Paddle, paddle2: &Paddle) {
+        if self.y <= 0 || self.y + BALL_SIZE >= SCREEN_HEIGHT {
+            self.dy = -self.dy;
+        }
+
+        if self.x + BALL_SIZE >= paddle1.x
+            && self.x <= paddle1.x + PADDLE_WIDTH
+            && self.y + BALL_SIZE >= paddle1.y
+            && self.y <= paddle1.y + PADDLE_HEIGHT
+        {
+            self.dx = -self.dx;
+            self.dy = -self.dy;
+        }
+
+        if self.x + BALL_SIZE >= paddle2.x
+            && self.x <= paddle2.x + PADDLE_WIDTH
+            && self.y + BALL_SIZE >= paddle2.y
+            && self.y <= paddle2.y + PADDLE_HEIGHT
+        {
+            self.dx = -self.dx;
+            self.dy = -self.dy;
+        }
+
+
+        if self.x + BALL_SIZE <= 1 + BALL_SIZE {
+            self.x = SCREEN_WIDTH / 2 - BALL_SIZE / 2;
+            self.y = SCREEN_HEIGHT / 2 - BALL_SIZE / 2;
+            self.dx = 1;
+            self.dy = 1;
+        }
+        
+        if self.x >= SCREEN_WIDTH - BALL_SIZE - 1 {
+            self.x = SCREEN_WIDTH / 2 - BALL_SIZE / 2;
+            self.y = SCREEN_HEIGHT / 2 - BALL_SIZE / 2;
+            self.dx = -1;
+            self.dy = 1;
+        }
+        self.x = (self.x as i16 + self.dx) as u16;
+        self.y = (self.y as i16 + self.dy) as u16;
+    }
+}
+
+static SPRITE_POSITIONS: [GbaCell<u16>; 6] = [
+    GbaCell::new(0),
+    GbaCell::new(0),
+    GbaCell::new(0),
+    GbaCell::new(0),
+    GbaCell::new(0),
+    GbaCell::new(0),
+];
+
+#[panic_handler]
+fn panic_handler(_: &core::panic::PanicInfo) -> ! {
+  loop {}
+}
+
+#[no_mangle]
+fn main() -> ! {
+    DISPCNT.write(
+        DisplayControl::new().with_video_mode(VideoMode::_3).with_show_bg2(true),
+    );
+
+    RUST_IRQ_HANDLER.write(Some(draw_sprites));
+    DISPSTAT.write(DisplayStatus::new().with_irq_vblank(true));
+    IE.write(IrqBits::VBLANK);
+    IME.write(true);
+
+    let mut left_paddle = Paddle::new(10, SCREEN_HEIGHT as u16 / 2 - PADDLE_HEIGHT / 2);
+    let mut right_paddle = Paddle::new(SCREEN_WIDTH as u16 - 10 - PADDLE_WIDTH, SCREEN_HEIGHT as u16 / 2 - PADDLE_HEIGHT / 2);
+    let mut ball = Ball::new(SCREEN_WIDTH as u16 / 2, SCREEN_HEIGHT as u16 / 2);
+
+    loop {
+        left_paddle.update();
+        right_paddle.update();
+        ball.update(&left_paddle, &right_paddle);
+
+        SPRITE_POSITIONS[0].write(left_paddle.x);
+        SPRITE_POSITIONS[1].write(left_paddle.y);
+        SPRITE_POSITIONS[2].write(right_paddle.x);
+        SPRITE_POSITIONS[3].write(right_paddle.y);
+        SPRITE_POSITIONS[4].write(ball.x);
+        SPRITE_POSITIONS[5].write(ball.y);
+
+        VBlankIntrWait();
+    }
+}
+
+extern "C" fn draw_sprites(_bits: IrqBits) {
+    unsafe {
+        let p = VIDEO3_VRAM.as_usize() as *mut u8;
+        __aeabi_memset(p, 240*160*2, 0)
+    }
+
+    draw_rect(SPRITE_POSITIONS[0].read(), SPRITE_POSITIONS[1].read(), PADDLE_WIDTH, PADDLE_HEIGHT, Color::WHITE);
+    draw_rect(SPRITE_POSITIONS[2].read(), SPRITE_POSITIONS[3].read(), PADDLE_WIDTH, PADDLE_HEIGHT, Color::WHITE);
+    draw_rect(SPRITE_POSITIONS[4].read(), SPRITE_POSITIONS[5].read(), BALL_SIZE, BALL_SIZE, Color::WHITE);
+}
+
+fn draw_rect(x: u16, y: u16, width: u16, height: u16, color: Color) {
+    for i in 0..width {
+        for j in 0..height {
+            VIDEO3_VRAM.index((x + i) as usize, (y + j) as usize).write(color);
+        }
+    }
+}